Spin-torque oscillator, a magnetic sensor and a magnetic recording system

A spin-torque oscillator comprising:

• a first ferromagnetic layer;
• a non-magnetic layer stacked on the first ferromagnetic layer;
• a second ferromagnetic layer stacked on the non-magnetic layer;
• a pair of electrodes configured to perpendicularly apply a current onto each plane of the first ferromagnetic layer, the non-magnetic layer and the second ferromagnetic layer, the current inducing a precession of a magnetization of at least one of the first ferromagnetic layer and the second ferromagnetic layer, the at least one of the first ferromagnetic layer and the second ferromagnetic layer being formed by an in-plane magnetization film having a uniaxial magnetic anisotropy;
• and
• a magnetic field generator configured to generate a magnetic field to control a direction of the magnetization so that a non-linearity frequency shift of the precession by the uniaxial magnetic anisotropy cancels a non-linearity frequency shift of the precession by a demagnetizing field on the in-plane magnetization film.